Blastocystis hominis grows well on only one of the media developed for protozoan cultivation. This is a biplasic (solid-liquid phases) egg slant, Locke's solution overlay, tubed medium. To this is added 30% serum. It is of course an empiric medium. The purpose of the present study is to develop a defined (synthetic) monophasis (liquid) medium for Blastocystis hominis that will allow adequate growth in serial passage. Progress: We are trying all of the serum-free media formulations that we can find, a new fatty acid mixture (Soy Bean Lipids, Boehringer Mannheim), and a new water soluble cholesterol. There is so little time to devote to this project that we are trying a shot-gun approach to devise a practical monophasic liquid synthetic medium for suspended culture of Blastocystis hominis.